In one type of conventional optical fiber connector, optical fibers to be connected are secured within central bores of precision ferrules, and the ferrules are aligned within a ferrule alignment assembly.
A commonly used ferrule alignment assembly comprises a split alignment sleeve retained in a housing. The alignment sleeve has an inner diameter which is slightly less than an outer diameter of the ferrules to be aligned and an outer diameter which is slightly less than an inner diameter of the alignment sleeve carrier, so that the alignment sleeve expands radially on insertion of the ferrules into the alignment sleeve and exerts radially inward force to bring the ferrules into axial alignment.
The ferrules are mounted within ferrule carriers which include bayonet or threaded fittings for mating with complementary fittings on the housing to secure the ferrule carriers to the housing. The ferrules are mechanically coupled to the ferrule carriers by helical springs which permit limited axial and angular movement of the ferrules within the ferrule carriers so that the ferrules can be brought into butting alignment within the alignment sleeve when the ferrule carriers are secured to the housing.
Blind mating variants of conventional ferrule-type optical connectors have been developed for making optical connections between circuit cards and backplanes in equipment racks. The known blind mating connectors have one part which mounts to a rear edge of the circuit card and another part which mounts to the backplane, the two parts coming together to make an optical connection when the circuit card is inserted into an equipment rack to which the backplane is mounted. A first of the two parts includes an alignment sleeve carrier and an alignment sleeve into which a first axially sprung ferrule protrudes. A second of the two parts includes a socket into which the alignment sleeve carrier slides when the two parts come together, and a second axially sprung ferrule which protrudes into the socket. The second ferrule enters the alignment sleeve for alignment with the first ferrule when the alignment sleeve carrier enters the socket.
In the known blind mating ferrule-type optical connectors, the helical springs which mechanically couple the ferrules to the ferrule carriers must absorb tolerances in the location of the circuit card relative to the backplane, the location of the connector parts on the card and backplane, and the location of the ferrules within the connector parts. The accumulated tolerances can be large enough to require the mounting of one of the connector parts to another helical spring which absorbs tolerances which cannot be absorbed by the helical springs which couple the ferrules to the ferrule carriers. This requirement for three helical springs of appropriate relative stiffness complicates design and manufacture of such blind mating connectors.
Moreover, accumulated tolerances can lead to significant variation in the force with which the combined helical springs bias the ferrules together when the connector is mated. The variation in the biasing force can cause variations in optical loss.
In many applications of known blind mating ferrule-type optical connectors, the fiber terminated in the ferrule of the card-mounted part is coupled to an optoelectronic device mounted on the card. The optical fiber between the optoelectronic device and the ferrule must be long enough to absorb bending due to movement of the ferrule within the card-mounted part during mating of the connector parts without breaking and without introducing unacceptably high bending losses. Normally this requires storage of a loop of fiber on the card.